Implicit learning is a phenomenon in which people acquire knowledge without intending to do so and without being able to describe that knowledge. Various indirect measures can be used to show that this information influences behavior. Since Reber's (1967) first report of implicit learning, a number of different researchers, using several different experimental techniques, have attempted to investigate this phenomenon. Recently, many of these techniques and the evidence obtained with them have been challenged. Past research left the theoretical distinction between implicit and explicit learning vulnerable to these challenges because it did not adequately distinguish implicit from explicit learning. The proposed research will do this by testing several specific theoretical propositions of the theory that explicit learning is mediated by structures in and around the hippocampus, those structures in the brain commonly identified as critical for conscious forms of memory, whereas implicit learning relies on other structures in the brain. Specifically, the proposed experiments will demonstrate that explicit knowledge depends on cognitive, or more complex, relational, forms of association, whereas implicit knowledge depends on noncognitive, less complex, nonrelational forms of association; that explicit knowledge is flexible and adaptive, whereas implicit knowledge is not; and that explicit knowledge is less prone to interference, whereas implicit knowledge is more so. A program of 20 experiments is proposed to these propositions.